Good sanitation can help you prevent bark beetles

By Ed Perry

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While driving in the county recently, I noticed several cases where piles of brush from last winter's pruning activities still were piled near the fruit trees.

It's a sure thing that any bark beetles or other borers that were present in the prunings would not have far to fly to reach the trees this spring.

While it's important to prune out weak and dying branches that may be diseased or infested with bark beetles, it is equally important to destroy such branches. Of course, not all branches are infested, but it's not worth taking a chance.

One of the worst infestations of bark beetles I can remember occurred in a home orchard where infested firewood had been piled near young fruit trees. Even though the young trees were well cared for and vigorous, several apricot, peach and plum trees were seriously damaged by the emerging bark beetles.

Sanitation is an important cultural practice around many woody plants, not only fruit and nut trees. Most conifers like pines, cedars and cypresses have their share of borer and bark beetle pests. So do other landscape trees and shrubs.

It's not a good idea to pile unseasoned, freshly cut wood near any woody plant, especially if the material was cut from dying or recently dead trees. Such wood is likely to attract or harbor wood-boring beetles.

If you want to store firewood that is suspect, especially near your fruit trees, be sure to cover and tightly seal the wood beneath clear plastic in a sunny location for several months.

The plastic tarp will keep out attacking beetles and prevent any from escaping the stored wood. It's important to properly prune off infested limbs and remove and dispose of dying trees so that boring insects do not emerge and attack other nearby trees. In many cases, it may be best to replace old declining trees.

Do not count on insecticides as a replacement for cultural methods when it comes to preventing borer infestations. Unless you can monitor your trees regularly in order to detect borer attacks just as they begin, any spraying is likely to be too late and ineffective.

Systemic insecticides are available and labeled for the control of certain borers on some tree species. Be sure to carefully read and follow the label instructions if you decide to use a pesticide for borer control. In most cases, even systemic pesticides will not reliably control or prevent attack by the various borers.

Sanitation is just one of several cultural methods you can use to prevent bark beetle attacks. In general, healthy plants are less likely to be attacked and are better able to survive the damage from a few boring insects.

The most important way of preventing borer attacks is proper irrigation. In most cases, trees that are being damaged by bark beetles and other borers are also suffering from drought stress.

You may want to consider planting ornamental tree species that are less subject to borer attacks. For instance, coast redwood and deodar cedar are not as seriously affected by bark beetles as are pines and cypresses. However, most deciduous fruit trees, including stone fruits, apple and other pome fruits, almonds and walnuts, are all attacked by bark beetles and other borers.

Ed Perry, a farm adviser with the UC Cooperative Extension, can be contacted at 525-6800 or ejperry@ucdavis.edu.